If you are a Drupal module developer, the easiest way to do this would be to define a custom field formatter that would specifically do this (i.e. linking field value to the URL of the node) for the text field and content type that you want.
If you are looking for a UI solution, I'd suggest installing the
custom_formatters module. Once you have done that, import the formatter below.
$formatter = new stdClass();
$formatter->disabled = FALSE; /* Edit this to true to make a default formatter disabled initially */
$formatter->api_version = 2;
$formatter->name = 'string_to_link';
$formatter->label = 'string_to_link';
$formatter->description = 'Converts string from a text field attached to a node to a link';
$formatter->mode = 'token';
$formatter->field_types = 'text';
$formatter->code = '<a href="[node:url]">[node:title]</a>';
$formatter->fapi = '';
Now, go to the "Manage Display" page of the content type where you have your Node title field, and set the formatter to *Custom: (string_to_link)*. The value of the field is immaterial now. It'll be linked to the node always.
However, linking to the node from the node view itself is not really of much use, right? So, I'm guessing you'd want this in a node listing. (A set of nodes). In that case, you might want to use the
Views module where you can explicitly link the node title to its URL for a view.